Method and device for detecting and locating ores in an electromagnetic way



11,678,49 K. SUNBERG HE'XHOD AND DEVICE FOR DETECTING AND LOCATING ORES IN AN ELECTROMAGNETIC WAY Filed Feb. 5, 1925 ATTORNEYSv Patented July 24, 1928 KARL SUNDBERQ OF RASUNDA, SWE

MALMLETNIN G, OF STOCKHO METHOD AND DEVICE roe, DETECTING- .enn noca'rme meennrrc WAY.

Application filed February 5, 1925, Serial No. 7,113, and in This invention '1' elates to the detecting and locating of ore bodies.

More particularly, it

relates to an electromagnetic device for detel-mining the changes produced by an ore body upon an electromagnetic field generated ,tion of the di in the territory or a method of locat of such a device.

to be prospected, and ing orebodies by the use Various devices have hitherto been employed for locating ore bodies electromagnetically by detecting the direction and magnitude of disturbances produced upon an electromagnetic field by a-body of ore. Or-

dinarily,

such devices comprise means for generating an electromagnetic field of calculated strength and means for detecting the effects caused by a body of ore upon this field. Such a is operated at detecting or pick-up circuit various points throughout the area to be investigated, and the results obtained at the several points are plotted to indicate the location of the ore body.

Present devices which determlnes units. That is,

employ a pick-up circuit the magnitude and direcsturbances directly in absolute the value of the generated field and the magnitude and direction of the disturbances at th the pick-up circu mined by noting their effect c various points at which it is operated are deterupon a galvanometer and from the deflections obtaining the absolute valu disturbances.

e of the. electromagnetic The underlying principles of an electromagnetic system for locating or described as follows.

At any given point in the area to be investigated, analternating electromag wire circuit usuall The field thus produced is generally termed the primary field.

within the anflue'nce be induced, which of their own, a s

netic field is set up in ay placed upon the ground.

In any ore bodies lying of this field currents will in turn will set up a field econdaryfield. The 'field actually existing in the area is then a combination of the primary and secondary fields and it is. this resultant field which forms the basis for the operation means which may of any detecting be used.

The detecting means usually comprises a device possessing solenoid or the lik inductive properties, as a e, and amplifyingand-de es may be.

DEN, ASSIGNOR TO AKTEBOLAGET ELEK TRISK LM, SWEDEN, A JOINT-STOCK COMPANY.

ORES IN AN ELECTRO- Sweden October 18, 1928.

tecting instruments. The solenoid when placed at various points in the region of the resultant field produces feeble reactions which, when amplified, can be readily noted on a detecting instrument, suchas a galvanometer. At each point at which the pick-up device is operated, the effect of the resultant field upon the solenoid is indicated directly. That is, produced by the galvanometer when the device is in a region of greater field strength. It is thus evident that if the frequency and intensity of the generated field has varied in value during the time that measurements have been made at different points throughout the area, the final results will not accurately determine the position of the ore body. It is therefore essential, with present detecting systems, that the frequency and intensity of the generated field be held constant, since the pick-up systems are all of the direct reading or absolute type. v To overcome such difficulties, since experience has shown that it is extremely difficult to maintain a generated field at substantially constant value, I have constructed a device and developed a method whereby the indications of the pickup apparatus may be made independent of any variation in the generated field. In other words, I have 1n" vented a pick-up system and a method which determines the location of an ore body by comparative readings instead of by direct readings.

In general, my invention comprises the use of a greater deflections will be I primary field generating means and.

a pick-up system employing two loops or mary fieldI may arrange-one of the loops of my pick-up system. At another point, arranged at some distance from the wire circuit I. may set up the other loop of my pick-up system. Since the first loop is located so close to the origin of the primary field that no appreciable influence will be evident from the secondary field, the first loop may be brought to a balance and a reading of resultant field strength obtained which reading will be substantially the same as that calculated for the primary field.

The second loop may then be brou ht to a balance to indicate the strength and direction of the resultant field at that point, and then the two loops may be balanced against each other. Since the value of the primary field is known and since the' two loops are identical, or, if not so, their conversion constant can readily be calculated, the value of the resultant field at the point at which the second loop is located can readily be determined in terms of the primary field strength as a unit..

After the value of the field in terms of the primary field has been determined for the position of the second loop, the first loop may be moved to that point and the second loop moved to a new point. The same balancing operations may then be repeated and the value of the field at the new point determined in terms of the primary field as before. Since the value of the field at any point is thus calculated in terms of the primary field as a unitas 1.5 units, 2.6 units,

' etc.it follows that any variation in the a strength and frequency of the primary field will not produce an error in the point to point determinations, inasmuch as the primary field is used only as a unit and while the value of the unit may change, the ratio will not. That is, if the value of the primary field is reduced, the value of the resultant field is also reduced, but it will always remain as so many units or fractions of units of the primary field. The point to point determinations may thus be carried out from place to place throughout the area and the exact location of the ore body determined.

The invention can best be understood by referring to the accompanying drawings in which I have illustrated one embodiment of the invention. In the drawings:

Fig. 1 is a diagram of one form of wire circuit for generating the primary field,

Fig. 2 is a circuit diagram of one form of pick-up system in accordance with the present invention, 1

Fig. 3 is a diagrammatic illustration of the manner in which the pick-up system is used atvarious points to determine the location of-the bed of ore.

Fig. 4 is a diagrammatic representation of the manner in which the two loops of one form of the pick-up system are balanced against each other,

Fig. 5 isa circuit diagram showing a variable inductance in parallel with one of the loops,

Fig. 6 is a circuit diagram showing a variable inductance in series with one of the loops,

Fig. 7 is a circuit diagram showing a vari able resistance in series with one of the loops,

Fig. 8 is acircuit diagram showing a variilble resistance in parallel with one of the cops V Fig. 9 is a diagram of a modified form pit (iivire circuit for generating the primary Fig. 10 is a diagram of another form of wire circuit for generating the primary field,

Fig. 11 is a vertical elevation of the electromagnetic field of an ore body showing 7 the direction of the field at the points as, 3 and 2,

Fig. 12 is a perspective View of a form of loop, in accordance with the invention.

Considerin the drawings more in detail, the primary field may be produced by laying an insulated cable on the ground in the form of a rectangle, as shown at ABCDE Fig. l, and connecting the ends of the cable AB to the terminals of an alternating current generator G. The field thus generated will penetrate into the surrounding area in the manner already described.

The primary field may also be generated by a galvanic circuit shown in Fig. 9. In this instance, the ends of the wire AB are thoroughly grounded and a generator inserted between the two ends. Still another manner of generating the field is shown in,

as illustrated in Figs. 1 and 9. Regardless of which type of wire circuitis employed in generating the field, the lines of force will penetrate to any ore body in the vicinity and will set up secondary currents producing a secondary field modifying the primary field and forming a basis for the comparative determinations made with a pickup circuit.

One form of the pick-up circuit which I use in making the comparative determinations is shown in Fig, 2. Two rotatable loops or coils of wire I and II connected in opposition to each other, have inserted in their common connecting leads, an amplifier V and a detecting instrument such as a telephone receiver T. When either of the loops is placed in the sphere of influence of an electromagnetic field "and slowly turned, the maximum sound will be heard in the receiver when the coils of the loop cut the greatest number of lines of force; that is, when the plane of the loop is perpendicular ore bodies believed to be turned to determine the to the lines of force or direction of the field,

and no sound will be heard when the plane of the loop is parallel to the direction of the field.

If-a given area is to be investigated in order to determine the location of certain present, the primary field generating circuit is laid out and one of the loops of the pick-up circuit arranged very close to the cable forming part of the-circuit. The other loop is temporarily disconnected. The first loop is then slowly turned until no sound is heardin the receiver. The plane of the loop is then par allel to the direction of the field. The loop is then turned perpendicular to the field and disconnected. Since the strength of the field is known at that point from the calculated strength of the primary field and since the direction has just been determined, both quantities are known for that particular location.

The second loop is then connected in circuit at any desired distant point and slowly direction of the field at that point. The first loop is then reconnected and the second til the sound in the receiver disappears. The angle between the plane of the second loop in its new position and its previous plane position is the'angle which indicates the compensation which is necessary between the two loops when located at those ,two points at which the determinations were made.

' represented by the arrow R. The angle through which the second loop is turned to provide compensation is indicated by oz.

After the two loops have been properly balanced and the magnitude of the angle a determined, the results are tabulated. first loop is then moved to the position formerly occupied by the second loop and the second loop is moved to a new point and the operation repeated. After each balancing, the first loop is moved to the position of the second loop and the second loop moved to a new position until enough points have been spotted about the area to accurately V determine the location of the ore body.

The manner in which the strength and direction of theprimary field, as determined by the first loop in its initial position, and the various succeeding angles a are employed to determine the location of the ore gody may be describedwith reference to ig. 3. j The strength and direction of the primary field at an initial point, such asw, is plotted as a vector P of suitable length, since both terms of P as a unit.

loop .turned un-- The The value of the second loop when as y while the first is then substituted quantities are known. angle 0:, obtained by the located at any point such loop was at the point at, in the equation I P Sin 0:.

VVherein P=strength of the primary field. 7s=conversion contant for the two loops, which is l if the two loops have the same number of turns or coils of wire.

And R=strength of the resultant field at the point at which the second loop is located. Since P is known and a and 7c are known, the value of R can be readily calculated in This value of R is then plotted as the vector R at the point 3 and given the direction'which was determined as the direction of the field at that point by the loop II, as previously explained. The value of the primary field is then plotted at g as the vector P of calculated length and direction as at w and the vector S determined by analysis. The direction which the vector S rection of the secondary field at the point 3 and by measuring the length of the vector the strength of the secondary field can be calculated in terms of P as a unit, regardless of the actual value of P at the time the determination was made.

When the first loop is moved to the pointy and the second loop to some point such as a and the direction of the resultant field and angle 0: again determined, the results are plotted for that point and the strength and direction of the secondary field obtained as before. The value of P in the equation will be the value of the previous B and the value of R will be the value of R By repetition of the above procedure the results for all of the succeeding points may be plotted in the same manner. The prolongation of all the secondary field vectors plotted at the various points will of the ore bed, which point willbe the point at which the vectors all converge. The primary field generating circuit may then "be moved to a new point and the calculations repeated. Since all of the constants of the generating wire circuit are known the value of P can be readily calculated for any points such as 3 and got Fig. 3. For level surfaces, the 'direction of the always be perpendicular to the surface of the ground.

The axis about which the loop is rotatable is perpendicular to the direction of the field to be determine Sometimes only a component of the total resultant field is investigated, in which case the loops are turned about an axis perpendicular to this component. If the horizontal component is to be determined they are rotated about their vertical axis, and about their horizontal axis if the vertical component is investigated. As

assumes will be the di determine the location primary field will I this rotation possible.

Instead of turning the loop 11 to bring about a balance and thereafter noting the angle a, a variable inductance or variable resistance may be connected in the circuitof the second loop, as indicated in Figs. 5, 6, 7 and 8. When the inductance or resistance is used, the loops areleft in the osition shown in Fig. 4 by the full, line 0 loop I and the dotted line of loop II, which is the position of maximum sound, and the inductance or resistance varied until the sound disappears. By noting the value of the inductance or resistance left in circuit, to produce the balance,-the ratio between the two field strengths can be readily determined by substitution of the value of the inductance or resistance in a suitable equation. The operation is then repeated for the diiierent points and the results plotted as before.

' ratio between the where is The formula employed, when an impedance is used for balancing the loops, corresponds to the formula previously mentioned and may be stated as a'n-equation.

P=Rlmp. 1

Wherein Z=the conversion constant for the two loops.

m=value of impedance in minimum position.

p=correction factor, which can be determined by investigating afield of known strength. r

- The manner in which the inductance or resistance is inserted in the loop circuit may vary for difierent conditions. Thus, the inductance may be connected in parallel as shown in Fig. 5 or in series as shown in Fig. 6, or the resistance may be connected in either series or parallel as shown in Figs. 7'

and 8. In all cases where either theinductance or resistance is used, the balancing is effected by varying the value of these quantities instead of by varying the position of the loop.

Usually, it will be found that the resultant field will be in phase with the primary field. Should, however, conditions arise wherein the two fields are out of phase to any appreciable extent, the in-phase component of R is used in the calculations by means of the equation I 'P=Rk sin 0: cos the phase angle, the other values being already explained. The ratio determined by the two loops will then be'the phase component cos of the resultant field. The value of the secondary field then determined by vector analysis will be the primary field and the in-v value of that 'partfof the secondary field which is in phase with the primary field.

The use of a variable inductance or resistance in the circuit of one of the loops is particularly advantageous for such out of phase conditions as have been mentioned because by a proper manipulation of the value of the inductance or resistancethe pha:e difference can be compensated and a more accurate determination of the silent point of the receiver can be made. As a result, more accurate readings will be obtained and the location of the ore body determined with greater exactness. I

I claim:

1. A device for determining the ratio of two simultaneously observed strengths of a resultant field produced in the territory of a generated terrestrial alternating electromagnetic field by ore bodies located within the influence of the generated field, comprising two rotatable ld ops connected to each other and adapted to be placed at two difl'erent points of said field, an amplifier: connected in the common circuit of said loops. and ourrent detecting means connected tosaid am- 2. A device for determining the ratio of two simultaneously observed strengths of a resultant field produced in the territory of a generated terrestrial alternating electromagnetic field by ore bodies located within the influence of the generated field, comprising two rotatable loops connected to each other and adapted to e placed-at different points in said field, one of said loops being adapted to be rotated to compensate for the influence of said, field upon the other-of said loops, an amplifier connected in the common circuit of said loops, and an electromagnetic current detecting device connected to. said amplifier.

3. A device for determining the ratio of two simultaneously observed strengths of a resultant field produced in the territoryof a generated terrestrial alternating electromagnetic field by ore bodies located within the influence of-the generated field, comprising twoloops connected to each other and adapted to be placed at two different points in said field, means for varying the influence of said field upon the circuit of one of said loops to compensate for the influenceof'said field upon the other-of said loops, an amplifier connected in the common circuit of said loops, and current detecting means connected to said amplifier.

4. A devicefor determining the ratio of two simultaneously observed strengths of the components of a resultant field produced in the, territory of a generated terrestrial alfield, comprising two loops connected-to each other, an amplifier connected in the tWo different any number of distant points in terms of the common circuit 7 -.detect1ng means of said loops, and current connected to said amplifier.

5. In a method of electromagnetically detecting and locating ore bodies, the steps comprising generating a terrestrial alternating electromagnetic" field, and determining the ratio of two simultaneously observed strengths of the resultant field produced at points by ore bodies located within the influence of said generated field.

6. In a method of electromagnetically detecting and locating ore bodies, the steps comprising generating a terrestrial alternat- -1ng primary field to induce a secondary alternating electromagnetic field in ore bodies located within the influence of said primary field, determining the strength of the resultant 0:? said primary and secondary fields at one point, and determining the strength of said resultant field at anotherpoint in terms of the resultant field strength at said first-mentioned point as a unit.

7 In a method of electromagnetically detecting and locating ore bodies, the steps comprising generating a terrestrial alternating primary field to induce a secondary alternating electromagnetic field in ore bodies located within the influence of said primary field, determining the strength and direction of said primary field at a point adjacent to the point of generation of said primary field, and simultaneously determining the strength of the resultant of said primary and secondary fields at a di;tant point in terms of the strength of the primary field at said first point as a unit.

8. In a method of electromagnetically de-' tecting and locating 'o-re bodies, the steps comprising generating a terrestrial alternating electromagnetic field, and determining the ratio of two simultaneously observed strengths of the components of the resultant field produced by ore bodies located within the influence of said generated field.

9. A method of electromagnetically detecting and locating ore bodies, which comprises generating a terrestrial alternating primary field to induce a secondary alternating electromagnetic field in'ore -bodies located within the influence of said primary field, determining the strength and direction of said primary field at a. point adjacent to the point of generation of said primary field, and determining the strength of the resultant of said primary and secondary fields at strength of the primary field as a unit.

10'. A method of electromagnetically detecting and locating ore bodies, which comprises generating a terrestrial alternating primary field to induce a secondary alternating electromagnetic field in ore bod es located within the influence of said primary field, placing one of two loops at one point in the field determining the dlrectlon ofthe electron'iagn'etic resultant of the primary and secondary fields at that point, placing the other of the two loops at another point in the field, determining the direction of the resultant field at that point, connecting the two loops to each other, balancing said second loop against said first loop, determining the strength of the resultant field at said second point in terms of the resultant field at the first-named point as a unit, moving the first loop to the second-named point and the second loop to a new point, determining the strength of the resultant field at the new point in the same manner as before, and repeating the point-to-point movement for as -many different points in the field as may be desired;

11. In a. method of electromagnet-ically detecting and locating ore bodies, the steps comprising generating a terrestrial alternating electromagnetic primary field of known strength to induce a secondary alternating field in ore bodies located within the influence of said primary field,- placing one of two loops at a point adjacent to the point of generation of said primary field, determining the direction of the primary field at that point, placing the other of the two loops at a distant point in the field, determining the direction of the resultant of the primary and secondary fields at that point, connecting the two loops to each other, balancing said second loop against said first loop, and determining the strength of the resultant field at the secondice named point in the terms of the known primary field strength as a unit.

12. In a method of electromagnetically detecting and locating ore bodies, the steps comprising generating a terrestrial alternating electromagnetic primary field of known strength to induce a secondary alternating electroma gneticfield in ore bodies located within the influence of said primary field, placing one of two rotatable loops at a. point no adjacent to the point of generation of said primary field, said loop circuit including an audible detecting device, rotating said loop until no sound is heard in the audible detecting device, thereby determining the direction of the primary field at that point, placing the otherof the two loops at a distant point in the field, rotating said second loop until no sound is heard in the audible detecting device, thereby determining the 12 direction of the resultant field at that point,

and from the value of said angle, the strength of said primary field and the direction of said resultant field determining the strength of the resultant field at sai second point in 'terms of the strength of the primary field as a unit.

13. A method of electromagnetically detecting and locating ore bodies, which comprises generating a terrestrial alternating electromagnetic primary field of known strength to induce a secondary alternating electromagnetic field in ore bodies located within. the influence of Said primary field, placing one of two rotatable loops at a point adjacent to the point of generation of said primary field, said loop circuit includingan audible detecting device, rotating said loop until no sound is heard in the audible detecting device, thereby determining the direction of the primary field at that point, placing the other of the two loops at a distant point in the field, rotating said second loop until no sound is heard in the audible detecting device, thereby determining the direction of the resultant field at that point, rotating said first loop ninety degrees, thereby producing maximum sound in the audible detecting device, connecting the two loops to each other, balancing the. second loop against the first loop by rotating the second loop until the sound disappears, measuring the angle between the plane of thefsecond loop and the plane of the previously determined direction of the resultant field at that point, and from the value of said angle, the strength of "said primary field and the direction of said resultant field determining the strengthof the resultant field i at said second point in terms of the strength of theprimary field as a. unit, moving the first loop to said second-named point, moving the second loop to a new, point, determining the strength of the resultantfield at the new point in terms of the "strength of the primary field as a unit, in the same manner as the first determination, and repeating the point-to-point movement and determinations foras many different points in the field a3 maybe desired.

14. In a method of electromagnetically detecting and locating primary field as a unit. 7

comprising generatmg a terrestrial alterng primary field to induce a secondary alrnating electromagnetic field -in ore bodies located within the influence of said primary field, placing one of two loopsa't a point adjacent to the point of generation of said primary field, determining the direction of the resultant of the primary and secondary fields. at that point, placing the other loop at another point in the field, determining the direction of the resultant field at that point, balancing said second loop against said first loop, and determining the strength of the resultant field at said second point in terms of the strength of the resultant field at the first-named point as a unit.

. 15. In a method of electromagnetica-lly deore bodies, the steps comprising generating a. terrestrial alternating electromagnetic primary field of".

of said primary field, said loop circuit includin an audible detecting device common to bot loops, rotating said first-mentioned loop until no sound is heard in' the audible detecting device, thereby determining the direction of the primary field at that point,

placing the other of the two loops at a distant point 1n the field, rotating said second loop until no sound is heard in the audible detecting device, thereby determining the direction of the resultant field at that point, rotating said firstloopninety degrees, thereby producing maximum sound in the audible detectin device, connecting the two loops to eac other, balancing said second loop agaimt said first loo and determining the strength of the resu tant field at said second point in terms of the strength of the In testimony whereof I have signed my name to this specification.

KARL SUNDBERG. 

